
[Sponsors] 
October 9, 2012, 05:51 
problem in DNS in a pipe

#1 
Member
Hassan Nemati
Join Date: Apr 2012
Posts: 31
Rep Power: 7 
Hi guys
I am running a DNS code in a pipe. For laminar flow I have a problem. as you see in 2d plot of radial velocity at inlet, there are some strange number of velocity. it should be zero but it is not. I will appreciate any help. 

October 9, 2012, 06:20 

#2  
Senior Member
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 3,503
Rep Power: 40 
Quote:
are you solving incompressible flows? did you check the divergencefree constraint in each cell? Are you sure of the numerical stability contraints? From the figure it seems that the radial velocity accounts for the wall and the incipient boundary layer in a very low Re flow with plug velocity inlet, but I may be wrog ... 

October 9, 2012, 07:58 

#3  
Member
Hassan Nemati
Join Date: Apr 2012
Posts: 31
Rep Power: 7 
Quote:
I am so grateful for your answer. the Re=60 based on friction velocity. number of mesh is: r=30 theta=16, z=96. Yes this is for incompressible flow. the divergence is Ok. I am using the profile ((Re/4.)*(1. 4.*(rp(i))**2.)) for inlet which is analytitical solution. I put radial and tangential velocity 0 at z=0 . 

October 9, 2012, 09:46 

#4  
Senior Member
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 3,503
Rep Power: 40 
Quote:
After you have to refine the grid and see what happens, usually the small value in the normaltowall velocity component can be controlled. See also your threshold value in the pressure solver, can be to high. After that, you can check further by changing the inflow/outflow condition in a periodic condition, this way you can check the inner solution. 

October 22, 2012, 12:10 
how strange the velocity is? Can you email me and we can discuss furtherly.

#5  
New Member
kuihe
Join Date: Oct 2012
Posts: 1
Rep Power: 0 
Quote:


Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
3D Swirl flow in the pipe: convergence problem  Sachin U. Nimbalkar  FLUENT  5  December 22, 2016 02:34 
[ICEM] Using a hybrid mesh for a simple pipe  Udio_NT  ANSYS Meshing & Geometry  17  October 18, 2012 14:42 
simpleFoam convergence problems for pipe flow problem  Mike Graham  OpenFOAM Running, Solving & CFD  0  January 30, 2012 15:40 
Problem meshing very thin pipe  B. Hemmen  FLUENT  2  May 16, 2006 08:29 
DNS to Eigenvalue > Cauchy Problem. HOW?  RMG  Main CFD Forum  0  February 12, 2004 06:45 